The objective of these studies is to to identify causes of developmental changes in taste preference in the rat. Using salt (NaCl) preferences as a model system, two factors in early development will be examined which may affect intake and preference. The first is age-related changes in taste sensitivity which may contribute to changes in taste preference. The second is preweaning taste exposure which may influence adult taste sensitivity and/or preference. The proposed studies are based on our reent work indicating that immature rats express elevated preference for hypertonic saline solutions compared to adults, and that one factor likely to contribute to this elevated saline intake is a relative insensitivity of the weanling's taste system to hypertonic saline concentrations. The proposed studies involve developing behavioral paradigms for evaluating threshold and suprathreshold sensitivity to tastants in weanling and adult rats without reliance on preference or hedonic measures. These studies will then be extended to an examination of the contribution of early taste experiences to taste development. The long term objective of this project is to understand the causes of elevated salt preference because high salt intake in humans has been implicated in the development and maintenance of essential hypertension. In examining the normative development of salt sensitivity and preference we will utilize two techniques for assessing taste sensitivity----(i) an operant taste discrimination task; and (ii) a procedure which takes advantage of the high degree of concentration specificity of the "preexposure effect" in taste aversion conditioning. We will also compare the development of salt sensitivity to that of sour and sweet. Taste function of rats exposed to neonatal taste deprivation or selective taste exposure will then be examined to determine whether early experience influences the course of taste development. Reductions in taste stimulation will be accomplished by an artificial rearing procedure which uses chronic intragastric cannulas and allows rat pups to be reared in the total absence of nursing from Postnatal Days 4 through 18.